1. Field of the Invention
The present invention relates to radio-network control apparatuses and radio-network control methods, and more particularly, to a radio-network control apparatus and a radio-network control method which select a radio communication channel used for a radio network, according to an environment measurement in which the period of time during which a communication channel cannot be used because the carrier transmitted from another apparatus reaches a predetermined strength is measured.
2. Description of the Related Art
Communication methods used for constructing a radio local area network (LAN) system include the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) method. Communication methods used for constructing a wire LAN system include the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) method.
In a radio LAN employing the CSMA/CA method, a communication channel used for actual communication is selected among a plurality of communication channels which can be used for communication, and the selected communication channel is shared by a plurality of communication terminals constituting the LAN. The communication channel is selected according to the instruction of the LAN user or when it has the minimum receiving electric-field strength, which is called the minimum signal receiving strength, among the plurality of communication channels which can be used for communication. The communication channel having the minimum receiving electric-field strength is selected because it has a low possibility of signal contention with other LANs.
Each of the plurality of communication terminals constituting the LAN transmits data as a packet by using the carrier having the frequency of the selected communication channel. Each communication terminal detects the carrier before transmitting a packet to check whether the communication channel is clear. When the communication channel is clear, the terminal transmits a packet.
In this way, with the use of the CSMA/CA method, even if a plurality of communication terminals share one communication channel, data is positively transmitted and received in a network without generating collisions in the communication channel. The CSMA/CA method is suited to LANs having a transfer rate of about 1 Mb/sec to 10 Mb/sec.
As described above, in a radio LAN system employing the CSMA/CA method, a communication channel is selected according to the instruction of the user or when it has the minimum carrier receiving strength.
When a communication channel is selected according to the instruction of the user, however, if the communication channel specified by the user is being used by another radio LAN system, the period of time during which the communication channel is clear is short since communication performed by two different LAN systems may cause contention in one communication channel.
In such a case, even when each communication terminal in each radio LAN system checks whether the communication channel is clear by carrier detection before it transmits a packet, the communication channel is being used in many cases, and it takes a long time to start transmitting a packet.
When the communication channel having the minimum carrier receiving strength is selected, if noise transmitted from an electric unit such as a microwave oven frequently jumps in at such a level that a packet transmission is impeded, a packet cannot be transmitted promptly.
In other words, when a communication terminal of a radio LAN system detects the carrier before transmitting a packet to check whether the communication channel is clear, it is deemed that the communication channel is being used due to the noise. In such a case, a packet cannot be transmitted until the noise is eliminated.
As described above, when a communication channel is selected either according to the instruction of the user or when it has the minimum carrier receiving strength, a packet cannot promptly be transmitted in some cases. In such cases, the data transfer capacity of the radio LAN system is reduced for a predetermined period of time and data cannot promptly be transmitted or received.
Accordingly, it is an object of the present invention to provide a selection method and a communication apparatus which select a radio communication channel used for a radio network, according to an environment measurement in which the period of time during which a communication channel cannot be used because the carrier transmitted from another apparatus reaches a predetermined strength is measured.
The foregoing object is achieved in one aspect of the present invention through the provision of a radio-communication-channel selection method used in a radio communication system in which a plurality of radio networks share a plurality of radio communication channels, for selecting a predetermined radio communication channel among the plurality of radio communication channels and for setting it to the radio communication channel of a new radio network, the radio channel method includes a determination step of determining whether the ID of the new radio network to be structured is received; a measurement step of detecting radio-signal intensity for a predetermined time for each of the plurality for radio communication channels and of measuring the time when each radio communication channel is clear according to the detected signal intensity and a predetermined value for each of the plurality of radio communication channels when it is determined in the determination step that the ID of the hew radio network to be structured is not received; and a selection step for selecting the radio communication channel to be used for the new radio network to be structured, according to the time when each communication channel is clear, measured for each of the plurality of radio communication channels.
The foregoing object is achieved in another aspect of the present invention through the provision of a radio network apparatus used in a radio communication system in which a plurality of radio networks share a plurality of radio communication channels, for selecting a predetermined radio communication channel among the plurality of radio communication channels and for setting it to the radio communication channel of a new radio network the radio network apparatus includes antenna means; tuner means for tuning in to each of the plurality of radio communication channels input from the antenna means, for outputting a measurement signal for measuring radio-signal intensity, for extracting a packet signal from a received signal, and for outputting the packet signal; signal-intensity-measurement means for measuring the signal intensity of the measurement signal for each of the plurality of radio communication channels, output from the tuner means, and for measuring the clear time of each of the plurality of radio communication channels according to the result of the signal-intensity measurement; and channel selection means for controlling the tuner means so as to tune in to each of the plurality of radio communication channels and to output the measurement signal and the packet signal, for controlling the signal-intensity measurement means so as to measure the clear time of each of the plurality of radio communication channels according to the measurement signal output from the tuner means, the channel selection means also selects a radio communication channel to be used for the radio network according to the clear time of each of the plurality of radio communication channels, output from the signal-intensity measurement means.
The foregoing object is achieved in still another aspect of the present invention through the provision of a method for joining a predetermined network in a radio communication area where a plurality of adjacent radio networks which share a plurality of radio communication channel, the method includes including a detection step of detecting a radio network having a predetermined ID in the plurality of radio communication channels; and, when a radio network having the predetermined ID is detected in the detection step, a step of executing communication according to a beacon signal transmitted at a predetermined-time interval by a control station which controls the predetermined radio network.